clc;
clear;
A=[16,2,3,13;
    5,11,10,8;
    9,7,6,12;
    4,14,15,1];
E=eye(4);
E(3,1)=-2;
disp('------------------------')
E1=inv(E),
A1=E*A,
A2=A*E
disp('------------------------')
E1=sym(eye(4));
E1(2:4,1)=-A(2:4,1)/A(1,1),
A1=E1*A
disp('------------------------')
E2=sym(eye(4));
E2([1 3 4],2)=-A1([1 3 4],2)/A1(2,2),
A2=E2*A1
E=E2*E1;
A3=E*A
